The field of this invention relates to launching devices and more particularly to subsea pipeline pig launching devices.
Pipelines are frequently cleaned by launching objects into them and propelling those objects under pressure to a different point in the pipeline where the object known as a pig is captured. Pig launchers used in the past have been built sufficiently large to enclose several pigs which can be launched in sequence. One of the problems in the designs used in the past involving multiple pigs in a launcher is that they jam up against each other, precluding any pigs from being launched at all. Other devices have involved loading multiple pigs in a circular layout in a rotating barrel and sequentially aligning pigs with the launch outlet for ultimate release. These devices have also proven to be large and cumbersome and have required significant maintenance to ensure proper operation. Additionally, due to misalignment upon rotation of the cylinder with the launch passage, the pigs could also stick in such designs, thus requiring an overhaul of the pig launcher. Typical examples of pig launchers used in the past can be found in U.S. Pat. Nos. 5,873,139; 5,219,244; 4,709,719; and 4,401,133.
In the past multiple pig launchers have used spheres. Undirectional pigs such as bullet or cylindrical shapes or those that have multiple cup shaped bushings have been launched one at a time from housings. An object of the present invention is to launch a series of such undirectional pigs from a common housing.
What has been lacking in the previous designs is a simple, uncomplicated pig launching device which is capable of sequentially launching multiple pigs in a reliable manner. Additionally, what is also desirable, and is an objective of the present invention, is to configure the pig launcher components so that they can be assembled subsea by a remotely operated vehicle (ROV). Another object of the invention is to be able to use an ROV to install a multiple pig launcher subsea remotely from a platform and to retrieve the pigs onto the platformn. Those and other objects of the present invention will become more apparent to those skilled in the art from a review of the detailed description of the preferred embodiment below.
A multiple pig subsea pig launcher is disclosed. The pig launcher can be assembled on a production pipeline subsea with the aid of an ROV. In the preferred embodiment, the pigs are connected to each other and spaced apart by a spine. The pig launcher is configured to capture the next pig to be launched in such a manner that the spine behind it is in alignment with a shearing valve; for example, coiled tubing or wireline. Sequential valve operation shears the spine and applies pressure behind the pig to launch it from the launcher past the pig detector and onto a platform for recapture.